DEVELOPERS: change Vivien Didelot e-mail address

I am exclusively using my Gmail address for now on. Reflect this in
the DEVELOPERS file.

Signed-off-by: Vivien Didelot <vivien.didelot@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

DEVELOPERS

@@ -2344,7 +2344,7 @@ F:	package/pixz/
 N:	Vinicius Tinti <viniciustinti@gmail.com>
 F:	package/python-thrift/
 
-N:	Vivien Didelot <vivien.didelot@savoirfairelinux.com>
+N:	Vivien Didelot <vivien.didelot@gmail.com>
 F:	board/technologic/ts5500/
 F:	configs/ts5500_defconfig